Once it’s in your car though, it’s a different story. When I was a kid, my dad filled up his Dodge van on a very cold Denver day and then parked it in our heated garage.

The next morning the garage was submerged in about an inch of gasoline. It’s a miracle we didn’t have a fire!

The hypothesis is that gasoline, being highly volatile, expands and contracts to a high degree with temperature fluctuations, and so is denser — will weigh more per volume — when it’s cooler.
Since it’s bought by volume, you get more (by weight) for your money if you buy at night (or whenever it cools down in your area). Or so goes the hypothesis.

It seems to make sense to me; does anyone know for sure?

I watch the digital temp gauge drop (with engine off) 50 degrees vs increase 50 degrees from heat soak with electric fans on. Heat soak from exhaust system manifolds at 1200 degrees can damage engine control sensors, plastic, hoses, wiring gets brittle, or loss of coolant at overflow, etc.

2 or more minutes with engine off isn’t going to drain a good battery. High battery load items: interior heating/cooling system fans, Head lights, Engine Cooling fans. Turn parking lights on if in line, at drive through’.
Low Load Items: Stock radio’s do not take any power. No gain turning them off.
Myself, I added a manual radiator fan switch to cool down engine and coolant during long stops vs letting system max out to turn them on.
Most blown head gaskets on aluminum blocks are from overheating from repeated overheating overflows of small amounts till it gets air ingested creating hot spots.

The people with turbo chargers know the routine with cool down procedures before shutting down an engine to prevent damaging heatsoak. Inspection of radiators is more critical now as they are designed to work right to the edge when new. Any build up inside will kill your chances of survival.

You’ll notice in the Southern high heat belt, that squad cars left running controlling traffic will open hood to prevent overheating and damaging heat soak.
I do the same for years even pulling in to get fuel. Coolant is right at 200 degrees, and on a 100 degree day, it needs all the help it can get.

You’ll notice air drag is at prime right at the edge at 50 mph. So if you can take advantage of this speed w/o creating havoc, you win.
I cruise in 2nd if under 33 mph to maintain a controlling attitude for slowing and speeding up.

Any speed above 50 is dramatic drag resistance.
A standard Piper can lift off the runway at 65 -75 mph. Test with hand out the window.

You know your in the wrong gear if you cannot speed up at will w/o downshifting a stick manual. This hammers the engines rod and crank bearings when in the wrong gear. There is less oil pressure to help offset this torture.
Cruising in high at lower speed is fine if it’s basically coasting with no load.

I leave automatic out of over drive till up to freeway speed. Constant unlocking from slight stepping on fuel while in slow city traffic of torque convertor is the number one cause of tranny damage.
See all the cars lined up at the tranny shops?
Practice these steps in quiet areas of traffic before getting into real rush hour.

The other thing is the impatient people. I usually sit at a light with the trans in neutral and the clutch out. I think it reduces wear on the TO bearing…but that’s just me.

Just this morning at the very first light–one block from my house–in the instant it takes me to stomp on the clutch and shove it into first when the light goes green, the guy behind me was honking.

If I took another two seconds to restart the engine, he’d be out of his vehicle using a tire iron on my windshield!

I know, screw ‘em; but it’s just not something I’m comfortable with.